Ignitor & gas valve ok, intermittent ignition problem

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Old 10-17-12, 12:37 PM
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Ignitor & gas valve ok, intermittent ignition problem

I have a high effic LP furnace that has me scratching my head. No ignition, but voltage to the gas valve, so I replaced the valve. Still same problem, so I found a manometer. Pressure incoming 13, outgoing 10, which seems right on. So I wasted money on a gas valve. As my Dad always says, education is expensive. So I let it cycle a few times & suddenly it lit. Burned fine. Let it burn 10 minutes & cycle off. Called for heat again & it errored out on the safety after cycling 4 times with no ignition. Multiple tests has 50% success in ignition after one or two cycles of trying to light. Ignitor seems to glow perfect. When burner does light, it burns nice, pressure stays right at 10 where it should be. Orifice in tube by ignitor looked fine when I changed the gas valve. I gave it a scratch & toothpick treatment, but looked ok. Anything else it could be?
 
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Old 10-17-12, 12:52 PM
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I'd be looking at the gas pressure when it DOESN'T light.

Do you have other gas appliances ---- are they operating normally?
 
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Old 10-17-12, 01:08 PM
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Gas pressure on outlet side whether it lights or not is 10 as soon as the valve opens. Therefore I think I've eliminated the regulator, line, gas valve, and valve regulator. Another gas furnace is only other appliance. That is on a separate line from same tank. Working fine.

Since the cycle goes all the way to the ignitor & opening the gas valve, I've also eliminated the pressure switches. No flame at all most of the time, but when it does light it stays lit, so eliminated the flame sensor too. That's why I'm scratching my head on this one.
 
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Old 10-17-12, 02:46 PM
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Do the burners light off the hot surface ignitor or does the ignitor light a pilot light that lights the burners in turn?
 
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Old 10-17-12, 05:33 PM
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Clean your burners would be a good start.
 
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Old 10-18-12, 01:34 PM
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Burners light off the ignitor, no pilot. Last night I cleaned & exchanged orifice from first tube by ignitor with another tube. Still no diff. I'll take the advice to clean out the burner next. Thanks.
 
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Old 10-18-12, 02:28 PM
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If cleaning the burners doesn't work I'd replace the ignitor. Old ignitors can fail to get hot enough fast enough.
 
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